1. Technical Field
The present invention relates to a method for forming an aluminum nitride thin film having a high resistance to thermal shock and having a high density on a member used in a process for manufacturing a semiconductor.
2. Description of the Related Art
In a dry process for manufacturing a semiconductor, a high-reactivity halogenous corrosive gas such as a fluorine-containing gas, a chlorine-containing gas or the like is often used as a gas for etching and cleaning and, therefore, a member which is to come into contact with such a high reactive gas is required to have a high corrosion resistance.
As members other than the member to be processed, which would come into contact with the high corrosive gas, it has been found that a sintered body of aluminum oxide, aluminum nitride, aluminum oxynitride or the like is preferable since it has a high corrosive resistance against a halogenous corrosive gas.
In addition, the thin film forming technique for forming a thin film of aluminum oxide, aluminum nitride or aluminum oxynitride on an inexpensive member such as metal, carbon or the like using a flame spraying method, a sputtering method, or a chemical vapor deposition method has been recently developed.
On the other hand, it is known that aluminum oxide and aluminum oxynitride exhibit a higher corrosion resistance against a fluorine-containing gas than that of aluminum nitride, and Japanese Patent No. 3024712 (Patent Publication No. 1) discloses an Al—O—N series composite material containing aluminum nitride (AlN), aluminum oxide (AlxOy) and aluminum oxynitride (AlxNyOz) and a synthesis process for manufacturing it.
However, the thin film formed of aluminum oxide or aluminum oxynitride having a higher coefficient of thermal expansion than aluminum nitride has a low resistance to thermal shock and tends to be cracked and split. Japanese Patent Application Laid Open 2007-16272 (Patent Publication No. 2) discloses that it is possible to ensure the dimensional stability and mechanical strength of a thin film and decrease the number of cracks formed therein by forming a protection film made of aluminum nitride (AlN), aluminum oxide (AlxOy), aluminum oxynitride (AlxNyOz) or a combination thereof on a substrate made of pyrolytic boron nitride (pBN), pyrolytic graphite (PG) and/or boron nitride to which carbon is doped and applying a compression stress to the thus formed thin film. However, since whether a stress applied to the thin film is a compression stress or a tensile stress depends upon the coefficient of thermal expansion of the material used for forming the thin film, the teaching of Patent Publication No. 2 can be applied only to a material having a certain coefficient of thermal expansion.
Members used in a semiconductor manufacturing process such as a susceptor, clamp ring, heater and the like have recently been grown in sizes larger than φ 300 mm (twelve inches) and since a thermal stress applied to the member becomes larger along with the growth in size, it is difficult to use as material for forming these members a sintered body of aluminum oxide or aluminum oxynitride which, while exhibiting a higher corrosion resistance than that of aluminum nitride against a fluorine-containing gas, has a low resistance to thermal shock.
Further, even in the case of covering the surface of members used in a semiconductor manufacturing process other than the member to be processed with a conventional aluminum nitride thin film, the member becomes larger along with the growth in size of a wafer and it is therefore necessary to enlarge the size of the space of the chamber of the film forming apparatus. As a consequence, since a source gas for forming an aluminum nitride thin film has to travel a long distance up to the member to be processed, the source gas reacts before arriving at the member to be processed to form aluminum nitride particles. As a result, the aluminum nitride thin film formed on the surface of the member to be processed under the conventional thin film forming condition becomes a powdery film and an aluminum nitride thin film having a high density therefore cannot be formed.